1. Field of the Invention
The invention relates a method, an apparatus, a storage medium, a program, and a program product for generating image data of a virtual space viewed from a predetermined view point, to execute a predetermined game in an apparatus which is operated and controlled by a processor.
2. Description of Related Art
Conventionally, a game apparatus for providing a plurality of objects in an object space as a virtual three dimensional space, and for generating image data viewed from a predetermined view point in the object space, is known. The game apparatus is popular as a game apparatus for providing a so-called virtual reality to a player. For example, in case of a player enjoys piloting an own fighter plane with a game apparatus, the player enjoys making the own fighter plane (Hereinafter, it will be called a player plane.) controlled the player fly in the object space, and fighting with another fighter plane (Hereinafter, it will be called a target plane.) controlled by another player or a computer.
When the above-described game apparatus generates more realistic image data, the virtual reality of the predetermined game is improved. Therefore, the player can devote himself to the game and enjoy playing the game.
For example, as indicated in a game screen shown in FIG. 1, in accordance with a moving object such as a target plane 3 , a missile 2 fired at the target plane 3 and so on, a phenomenon of a particle system, such as a condensation trail 4a, a smoke 4b emitted from a missile propeller and so on, is represented. The above-described particle system object generated so as to attach to or follow the moving object is one of important factors in making the player feel speed of the player plane 1 and tension caused by the missile 2 fired at the target plane 3. Therefore, in order to improve a quality of the game, it has been an important technical object to generate more realistic image data of particle system objects in as light an operation load as possible and in as little a storage capacity as possible.
One of algorithms of generating image data of particle system objects such as a condensation trial and so on, according to an earlier development, is disclosed in, for example, Japanese Patent Application Publication No. Tokukai 2000-225274.
In the publication, as shown in FIG. 2A, one or a plurality of quadrilateral polygons PL are provided on a trail of the moving object such as the missile 2 and so on. As shown in FIG. 2B, the polygons PL are designed so that a characteristic color of each of the polygons PL is changed lighter and lighter toward an outer edge. Thereby, the polygons PL look not a mere quadrilateral, but as if they were a line which is a gathering of fogs.
Then, positional coordinates and speeds of the polygons PL are stored in an apparatus, and the apparatus generates image data of the polygons PL at predetermined frames. Thereby, the apparatus expresses a state the condensation trail and the smoke are generated with trails and left for some time.
However, although the particle system object itself such as the condensation trail, the smoke and so on, is realistically represented according to the above-described algorithm, it is impossible to say that the motion of the particle system object is represented sufficiently.
For example, in case of the fly of the missile, as shown in FIG. 3B, because real missiles 2-1 and 2-2 fired from the player plane 1 fly to the target plane 3 with controlling postures thereof respectively, the postures of the missiles 2-1 and 2-2 are always swung upward, downward, rightward and leftward. Therefore, the smokes 4b-1 and 4b-2 emitted from the missile propellers of the missiles 2-1 and 2-2 are affected by the postures of the missiles 2-1 and 2-2 when the smokes are emitted, and have speeds in various directions. As a result, although the smokes 4b-1 and 4b-2 float along the trail of the missiles 2-1 and 2-2 when the smokes are emitted, the smokes 4b-1 and 4b-2 move in random directions as time passes from diffusion to disappearance. When the smokes 4b-1 and 4b-2 are observed from far, the trails of the smokes 4b-1 and 4b-2 look like winding. In particular, at circular positions of the missiles 2-1 and 2-2, the phenomena that the smokes 4b-1 and 4b-2 flow with winding in opposite directions to the circular directions are caused.
However, according to the algorithm disclosed in the above-described publication, the motion itself of the smoke is taken into consideration. Therefore, as shown in FIG. 3A, the unnatural state the smokes 4b-1 and 4b-2 are generated exactly along the condensation trails and keep the generated shapes to disappearance, is represented. As a result, naturally, regardless of the exciting scene the missiles 2-1 and 2-2 fly to the target plane 3, there is a problem a player feel the expression of the game simple, and the player cannot feel quite satisfactory realistic and be excited.